1. Field of the Invention
The invention relates to xenon arc lamps and in particular to compact or handheld xenon short arc searchlights or illumination systems.
2. Description of Prior Art
Handheld lighting devices with focused beams or spotlights or searchlights, whether battery-powered or line-powered, are commonly used by military, law enforcement, fire and rescue personnel, security personnel, hunters and recreational boaters among others for nighttime surveillance in any application where a high intensity spotlight is required. The conditions of use are highly varied, but generally require the light to deliver a desired field of view at long distances, be reliable, durable and field maintainable in order for it to be practically used in the designed applications. Typically the light is hand carried and must be completely operable using simple and easily access manual controls which do not require the use of two hands.
In prior art xenon short-arc searchlights or illumination systems, whether handheld, portable or fixed mounted, the luminance distribution of the arc has been positioned facing in the direction of the beam (cathode to the rear), to provide a uniform beam pattern when the arc is at the focal point of the parabolic reflector. When the luminance distribution of the arc is positioned in this manner, a majority of the light output is collected in the low magnification section of the reflector and in a slightly divergent manner in the far-field. When the beam is diffused into a flood pattern, a large un-illuminated area or xe2x80x9cblack holexe2x80x9d is projected. Reversing the lamp position so that the full luminance distribution of the arc is in the high magnification section of the parabolic reflector produces a more concentrated beam in the near- and far-field and hence greater range can be achieved. Additionally, when the beam is diffused into a flood pattern no characteristic xe2x80x9cblack holexe2x80x9d of prior art configurations is produced. When the arc is moved slightly beyond (or slightly rearward of) the reflector""s focal point, the combination of a placing all available light in the high magnification section of the reflector and collecting it in a slightly convergent manner produces roughly twice the operating range as a conventional anode-forward device.
The operation of the xenon arc lamp requires a power supply capable of supplying a regulated current to insure ignition of the lamp and maintenance of its operation. Typically three voltage are required to ignite an arc lamp, bring it into operation and maintain its operation, namely: (1) a high voltage RF pulse applied across the lamp electrodes to ignite or break down the non-ionized xenon gas between the lamp electrodes; (2) a second voltage higher than the operating voltage of the lamp to be applied across the lamp electrodes at the time the high voltage radio frequency (RF) pulse is applied in order to establish a glowing plasma between the electrodes; and (3) a lower voltage to sustain the flow of plasma current at a level sufficient to create a bright glow after the lamp has been ignited.
In prior art battery powered searchlights, large high voltage transformers and large storage capacitors have been required to generate a high voltage current of sufficient magnitude to power the lamp""s ignition. A separate voltage boosting circuit for generating the second voltage to establish the plasma adds to the size, weight and component count of the lamp circuitry. The resulting circuitry in prior art has traditionally been less than optimum, with excessive energy lost to heat, and relegating battery running times to less than desirable.
Therefore, what is needed is an optical assembly to increase light collection efficiently and dissipate associated heat to produce a significantly more concentrated beam and a circuit topology by which the arc lamp regulated current can be supplied, but with a reduction in the size, weight and component count of the lamp circuitry and at high circuit efficiency to maximize battery life and minimize heatload.
The invention is a searchlight for generating a beam of light comprising an arc lamp, high-efficiency electronic ballast circuitry coupled to the arc lamp, a wide range power supply plus an internal battery and battery charger coupled to the ballasting circuit for powering the ballasting circuit and the arc lamp. A single converter circuit is used both for battery charging from an external power source and ballasting an arc lamp. In the illustrated embodiment the arc lamp is a xenon arc lamp, but it expressly is intended to include other kinds of plasma lamps, including without limitation metal halide and halogen lamps. In addition, although the invention is described in terms of a portable battery powered light, nonbattery-powered or line-powered lights in fixed configurations are within the express scope of the invention. For example, the use of the claimed light in aircraft and vehicular systems is included as is simple security lighting in a fixed site.
The invention is characterized as a searchlight comprising a lamp, a reflector disposed about the lamp to reflect light generated by the lamp, a lamp holder to position the lamp precisely along the reflector""s axis of optical symmetry, a reflector positioner so that the reflector is selectively moved by user with respect to the searchlight while the lamp remains fixed relative to the searchlight, and a lamp circuit coupled to the lamp for powering and controlling illumination produced by the lamp.
The lamp is a xenon arc lamp having an anode and cathode. The xenon arc lamp is mounted within the searchlight so that the anode of the xenon arc lamp is in the rearward position relative to the direction of a beam projected by the searchlight so that field illumination of the beam is slightly convergent and more concentrated and therefore delivers much longer range of operation. This orientation is unique in searchlight and illumination systems employing xenon short arc lamps.
The lamp is affixed in a lamp holder that allows precision alignment, and is designed to be quickly replaceable. The lamp module locks into a fluted heat sink to conductively dissipate lamp heat from the anode, as opposed to radiating heat in conventional anode-forward searchlights.
The reflector has an optical axis of symmetry. The lamp is positioned on the optical axis of symmetry. The reflector positioner moves the reflector in two opposing directions along the optical axis of symmetry. The lamp is radially adjustable relative to the reflector to be disposed on the optical axis of symmetry. The radial adjustment of the lamp on the optical axis is field adjustable. The reflector positioner retains the relative position of the reflector with respect to the lamp at a last relative position between the lamp and reflector which was selected when last using the searchlight. Thus, the design has a last use memory for the beam focus or adjustment.
The lamp, reflector, and reflector positioner are removable from the lamp housing as a unit to allow different reflector materials (for example nickel rhodium, aluminum, gold) to be easily substituted for maximum reflectivity depending on specific applications. The searchlight comprises a housing for containing the lamp, lamp circuit, reflector and reflector positioner.
The invention is still further characterized as a searchlight comprising a housing; a lamp disposed within the housing, a lamp circuit disposed within the housing, and a reflector disposed within the housing. The housing is characterized by a mounting fixture adapted to permit quick field coupling to a second device so that movement of the housing to direct the beam from the lamp is integrally manipulated with the second device.
The searchlight further comprises a searchlight housing in which the battery is included with the battery charging circuit, the ballasting circuit and the arc lamp as a single unit.
The electronic ballast circuitry is comprised of a converter and igniter. The converter has an output coupled across the arc lamp for providing a converted direct current (dc) current and voltage to the arc lamp. The igniter is coupled across the arc lamp to provide a high voltage RF ignition current to the arc lamp. The converter is controlled by a smooth variation of current and voltage to the arc lamp to correspondingly smoothly vary light output from the arc lamp between high and low intensities. By xe2x80x9csmooth variationxe2x80x9d it is meant that the changes in intensity of the lamp can be made very small so that they are not or are almost not visually perceptible by an ordinary human observer. The converter is controlled to provide the smooth variations between high and low intensities by a multiplicity of small digital current steps. Alternatively, the converter is controlled to provide the smooth variations between high and low intensities by an approximate or digitally simulated analog variation in current intensity provided to the arc lamp. The ballasting circuit is controlled by a control circuit to turn the arc lamp on after ignition at minimum intensity level of operation.
The searchlight further comprises a handle with a mounting formed as part of the housing to allow portability for the searchlight and for mounting to the second device. The mounting is a tripod mount so that the portable searchlight may be fixed in the field to a tripod with the second device. The mounting on the handle is a thumb screw mount to permit mounting of an optical detection device onto the searchlight and rigidly fixed to the housing.
The searchlight further comprises a field changeable filter disposed on the searchlight to select frequency ranges transmitted in the beam to a selected frequency range depending on application. The filter is selected to permit transmission of light in the beam through the filter for illumination in one of the environments comprised of illumination in a smoky environment, for infrared illumination, for underwater illumination, for ultraviolet or any specific color in the visible range. The filter can also be selected for reduction of intensity of the beam from the searchlight to present a minimum intensity output in the beam below which the arc lamp could not operate but for the filter.